Throw-away type air filters have been on the market for many years. These throw-away air filters have been made for both consumer and commercial use in HVAC systems. These inexpensive filters provide protection mainly for the HVAC system itself. These filters are provided so that large objects are captured before they cause damage to the fan motor and other components. In general, these low-efficiency filters were not intended to capture smaller particles of dust, pollen and mold that pass through to the indoor environment.
A very large number of permanent-type air filters have recently entered the market. These permanent type filters are generally made of a rigid aluminum frame. The filter material is received between two walls of expanded metal material. The filter material is made of a very pliable material having little or no interior strength. The expanded metal material can be used to form a honeycomb shape around the filter material. The expanded metal is used to support the filter material within the frame.
As an example, an "electrostatic" air filter is the subject of U.S. Pat. No. 4,902,306, issued on Feb. 20, 1990, to Burnett et al. This patent describes a filter which uses alternating layers of charged materials. Typically, these layers are in the form of woven polypropylene screens. This filter has some type of expanded metal or galvanized wire mesh on both sides. This expanded metal serves to support the interior filtering materials and to keep them contained within the rigid aluminum or plastic frames. The subject matter of this patent is typical of the various permanent-type filters which are presently on the market. Unfortunately, these permanent-type filters have several disadvantages.
Initially, these types of permanent-type filters have a high unit cost. This is due to the use of the relatively expensive items such as the woven polypropylene mesh and the expanded metals. Unfortunately, it is necessary that such materials be used in these air filters since the frames, themselves, are of a relatively weak nature. The frames do not have any means for holding the material in the frame directly. Without the expanded metal containment surfaces, the filtering materials would quickly and easily fall out of position from within the frame.
Another disadvantage is that the outer layers, particularly those of expanded metals, are abrasive to the hands. If it is necessary to remove the filter, these surfaces can scrape or cut. In general, the filter must be handled in a delicate fashion so as to accomplish the necessary periodic cleaning of the filter.
These permanent-type filters have no means with which to lock the layers of the filtering material within the frame. All of these frames rely on the strength of the various layers so that all of the materials stay within the frame. However, the filtering materials, in all of these systems, are normally some type of polyester fiber or foam. These materials can easily sag down over a period of time from the weight of the water which is used to clean the filter. If the polyester material (or other layers of material) does sag within the frame, then there will be a significant gap between the filter media and the frame, through which unfiltered dust and contaminants will flow past the filter.
The frames which are used for the conventional types of permanent-type filters are usually made of an aluminum material. When this aluminum frame is inserted within the housing of the HVAC system, then a significant amount of vibration can occur. Any annoying noises which a permanent-type filter would cause, when installed, would quickly dissuade persons from using such systems. In addition, such vibration can cause the dirt contained in the filter to be discharged into the plenum.
The frames which are used on permanent-type air filters do not usually have any means for an air-tight seal in that area where the frame meets the filter housing of the HVAC system. Without an air-tight seal, the air can pass around the frame and into the air plenum. Wherever the air can pass freely, it will allow a significant amount of dust or other contaminants to flow around the frame and filtering materials (which were intended to capture these particles).
As such, it is an object of the present invention to provide an air filter that is of relatively low cost.
It is another object of the present invention to provide an air filter which avoids the use of expanded metal support surfaces.
It is a further object of the present invention to provide an air filter which effectively retains the filter material in its proper position within the frame.
It is still a further object of the present invention to provide a vibration-resistant frame.
It is another object of the present invention to provide a frame which effectively creates an air-tight seal between the frame and the filter housing.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.